Light activated internal sizing of paper



United States Patent Oflice U.S. Cl. 162-179 5 Claims ABSTRACT OF THE DISCLOSURE This application relates to a method of internally sizing paper by mixing with an aqueous slurry of paper pulp 0.2% to 2.5% by weight, based on the weight of the dry pulp, of certain fatty acid condensation products, forming the thus treated paper pulp into sheets, and exposing the sheets to actinic light for a suflicient period to expose the sheets to at least enough radiant energy to achieve a sized paper having a lactic acid penetration time greater than 600 seconds and an ink flotation time greater than 900 seconds. For example, using ultraviolet light, which is preferred, the quantity of radiant energy should be at least about 6 10- wat1:-sec./cm. of radiant energy. The condensation products are further characterized by having at least 32% by weight of unsaponifiable matter and by having a mean molecular weight of at least 3 times that of the fatty acid.

BACKGROUND OF THE INVENTION Field of the invention This application relates to processes for the internal sizing of paper and particularly to such a process Wherein actinic light is utilized to activate the paper size.

Description of the prior art This application is an improvement of the process described in copending, commonly assigned U.S. application of Charles E. Feazel, Ser. No. 637,933, filed May 12, 1967, now Pat. No. 3,404,064 and entitled Improved Method for the Internal Sizing of Paper. That application in turn was a continuaiton-in-part of commonly assigned U.S. application Ser. No. 299,157 of the same inventor, filed Aug. 1, 1963 and now abandoned.

The disclosures of both of these prior applications are incorporated herein by reference. The essentials of these disclosures are set forth in the paragraphs below.

The sizing agents of the two above-referenced U.S. applications may be produced according to the process described in U.S. Pat. 2,923,718. As disclosed in that patent, column 1, lines 69-72, it is preferred that R in the fatty acid formula RCOOH is an alkyl group having a chain length from 9' to 25 carbon atoms. As further disclosed by that patent the sizing agents of the present invention can be obtained by condensing such fatty acids in the presence of a catalyst selected from the group consisting of boric acid, boric oxide, ammonium pentaborate, trimethyl borate, triethyl borate, mannitol borate, and the mixed anhydrides of boric acid and fatty acid. As disclosed by the above-identified applications the sizing agents may also be prepared by condensing at least one fatty acid in the presence of BF Examples of fatty acids useful as starting materials in the preparation of the fatty acid condensation products are oleic, stearic and linoleic acid.

The condensates thus produced are characterized by a substantial amount, preferably about 32%, of unspaonifiable matter, a low acid and saponification value, an increased iodine value as compared to the starting material and a high mean molecular weight. The mean 3,519,533 Patented July 7, 1970 molecular weight of the condensation product is roughly equal to or higher than the calculated molecular weight of a theoretical condensation product of 3 molecules of the fatty acid starting material.

As disclosed by the above-identified continuation-inpart application, the preferred condensation products have been found to be those prepared from fatty acid compositions of the type described above wherein at least about 40% of the acids are saturated C -C acids. An example of such an acid composition is Industrene 4022, a mixture of saturated fatty acids derived from fish oil by hydrogenation and saponification, sold by Humko Products Division, National Dairy Products Corporation. It has been found that condensation products prepared from acids of such chain lengths achieve acceptable paper sizing when applied in reduced concentrations fromthose necessary when condensation products of shorter chain fatty acids are used. Condensation products made from saturated acids have been found to be preferable to those made from unsaturated acids. Furthermore, it has been found that it is preferable to treat these preferred condensation products with hot alkali and remove the water soluble fraction thus produced before applying the condensation product to the paper pulp.

Basically, internal sizing using the above-described condensation products is accomplished by dispersing an emulsion of a fatty acid condensation product in an aqueous paper pulp slurry and depositing the condensation product on the pulp. An agent such as alum may be used to facilitate the deposition. The pulp, internally sized with the fatty acid condensation product, is thereafter formed into a sheet in a manner conventional in the paper industry.

Since the fatty acid condensation products are substantially insoluble in water they are preferably applied to the paper pulp as emulsions in order to provide an even distribution of sizing agent on the fiber of the pulp. A convenient procedure is to apply the fatty acid condensation product in the form of an aqueous emulsion. Such an emulsion is obtained by adding an emulsifying agent and an organic thickening agent, such as a cationic starch, to an aqueous dispersion of the condensation product. The emulsion is then added to the aqueous paper pulp with suflicient agitation to insure good distribution. The procedure for preparing the emulsion and depositing the size on the fiber is a matter of convenience and may be accomplished by any of the methods known in the art. For example the emulsion may be prepared by mixing the fatty acid condensation product with a soap, an emulsifying agent, or, preferably, a cationic starch, or mixtures of these, to form a suitable emulsion of the fatty acid condensation products. Examples of suitable emulsifying agents are polyoxyethylenesorbit'an ethers and carboxymethylcellulose. An example of a suitable starch useful in the preparation of a suitable emulsion is Cato 8, a product of National Starch Company. The use of starch is advantageous not only as an aid in dispersing the fatty acid condensation product but also because it aids in retaining the sizing agent on the fiber.

The pH value of the pulp slurry prior to the addition of sizing and precipitating agent may be varied over a Wide range from about pH 5 to pH 10. The pH of the pulp slurry may be conveniently adjusted to within the range of 8-10 by the addition of an alkali medium such as a dilute solution of sodium carbonate or sodium hydroxide. Since the sizing is effective in the presence of alkali mediums, the paper may be advantageously sized in the presence of alkali fillers without a decrease of the folding strength or loss of water absorption qualities of the sized paper.

The following example of preparation of a fatty acid condensation product and application thereof as a paper size illustrates the above description.

A condensation product is prepared according to the method disclosed in US. Pat. 2,923,718. In accordance with this method oleic acid is heated to a temperature of about 220 to 290 C. for about 6 hours in the presence of a boric acid catalyst. The product is thereafter freed of unreacted acid by dissolving it in benzene, extracting the solution with aqueous sodium carbonate, then washing with water. The crude product which forms is a redbrown viscous oil having an iodine number of around 117 and a saponification number of about 112. It is insoluble in water and is preferably applied to the pulp in the form of an emulsion to insure uniform distribution onto the fibers of the pulp. The emulsion is prepared by mixing the condensation product with an emulsifying agent of a cationic starch such as Cato 8, and this emulsion is then added to the paper pulp slurry, for example in the beater of a paper making system. The mixture is then agitated to thoroughly mix the two masses. The amount of oleic acid condensation product applied to the pulp may vary from about 0.2% to about 2.5%, based on the weight of the dry pulp, depending on the requirements of the sized paper.

An example of a preferred embodiment of the method of making the condensation product and applying same disclosed in the above-referenced continuation-in-part application is set forth below.

Industrene 4022 starting material, described above, was heated gradually over a 48 hour period at reduced pressure to a temperature of about 300 C. with a boric acid catalyst. The product was then extracted with boiling alcohol. The resulting condensate had an acid number of about 3 and a saponi-fication number of about 10'. It was insoluble in water and was therefore applied to paper pulp in the form of an emulsion prepared in the manner described in the previous paragraph.

The preferred condensation products have been found to function particularly well as sizing agents when they are treated with alkali and the resulting water soluble fraction is removed before the condensation product is emulsified and applied to the paper pulp. This alkali treatment can be effected, for example, by refluxing the condensation product for several hours with about 0.1 its weight of sodium hydroxide in about its weight of benzene and about twice its weight of alcohol and then washing the resultant solid residue with hot water to remove the water soluble fraction.

SUMMARY OF THE INVENTION Applicants have now discovered that, although the methods described in the two prior applications referred to above yield paper which is sufficiently sized so as to have useful characteristics, a far superior sized paper is obtained by the use of light to activate the paper size.

Although some small degree of exposure of the fatty acid condensate sizing agents to ordinary room light was inherent in the above-mentioned previous paper sizing processes, applicants have now discovered that that degree of exposure to that type of light was insuflicient to consistently produce under practical conditions the unobvious and unexpectedly superior paper size of the present invention or even to make obvious to one ordinarily skilled in the art that light had an effect on the sizing agents.

Any form of actinic light, with sufficient exposure is suitable to activate the paper sizes of this invention. For example light from an ultraviolet mercury arc lamp, from a sun lamp and from a photoflood lamp have all proved to be suitable to activate the sizes of this invention. However, these are merely examples of types of actinic light which can be used and are not meant to limit applicants invention to these types of light.

We have found that the paper sheets should be exposed to sufficient radiant energy to size the paper to achieve an ink flotation time in excess of 900 seconds and a lactic acid penetration time in excess of 600 seconds.

,We have found that ultraviolet light is the preferred type of light for activating the sizes, since with ultraviolet light the desired sizing effect can be achieved with a much smaller application of energy per unit area of paper to be sized. By ultraviolet light we mean light having a Wave length of from about 350 to about 375 millimicrons. We have found that with ultraviolet light radiant energy of at least about 6 1(lwatt-sec./cm. applied to the paper must be used to achieve the desired paper size. Other types of light were found to require greater application of energy.

DESCRIPTION OF THE PREFERRED EMBODIMENT The following tables illustrate the effect of light in sizing paper treated in the manner previously described with the previous described condensation products. The degree to which the paper has been sized by the sizing process has been measured in terms of the Cobb size test, in terms of penetration time in seconds for a 10% lactic acid solution and also in terms of ink flotation time in seconds.

The latter method is described in detail in the book Pulp and Paper Chemistry and Chemical Technology, second edition, volume 3, by Interscience Publishers, Inc., of New York City (1960).

The method used to determine lactic acid solution penetration time was similar to a standard test of the Technical Association of the Pulp and Paper Industry (TAPPI) denoted T462-m-43. In the present adaptation of that test a sample of paper to be tested was placed on a piece of window glass and a hypodermic syringe without a needle was filled with a 10% aqueous solution of lactic acid colored with methyl orange indicator. A drop of the solution was allowed to fall into the paper from the tip of the hypodermic syringe and the time required for the drop to penetrate was measured with a stop watch.

An ink flotation time in excess of 900 seconds and a lactic acid penetration time in excess of 600 seconds is considered as indicating an acceptable paper size for the purposes of this application.

The Cobb size test is procedure T441 of the Technical Association of the Pulp and Paper Industry (TAPPI). In this procedure an area of the sheet to be tested is defined by clamping it under a metal ring 10 cm. in inside diameter and the ring is then filled with water. After a measured interval of time, usually 1-5 minutes, the water is poured off, the ring is removed, and the paper is blotted to remove surface water. The amount of water absorbed is determined by weighing the paper before and after exposure, and the Cobb size value is calculated and reported as grams of water absorbed per square meter of paper. The lower the Cobb size value, the better the sizmg.

Tables I and II indicate the distinct difference between papers sized while kept in the dark and papers exposed to light. Table II also compares paper sized by being exposed to concentrated light with paper exposed only to normal room light while being processed according to the method of the earlier applications referred to above.

Table III illustrates that the effect of light on the paper sizing condensates is not restricted to Industrene 4022 condensate.

Table IV compares the sizing effect of various types of light and illustrates why ultraviolet light is the preferred form of actinic light.

Table V indicates the effect of various amounts of radiant energy on the paper sizing condensates. It illustrates why a minimum total energy of about 6X 10- wattsec/cm. is necessary to achieve acceptable sizing of the condensate treated paper.

TABLE I Sizing Properties 1 Penetration Penetration time, seconds, time, seconds, without light with light exposure exposure 2 Saponi- 107 107 Acid iication mu lacti Reactant Catalyst No. N 0. acid Ink acid Ink Industrene 4022 "B oron trifluoride etherate 6 20 2 600 900 1 Handsheets were prepared from 85-brightncss krait pulp, sized with 0.5% by weight condensation product of the reactant.

2 The handsheets were exposed to a General Electric RS Reflector Sunlamp for 30 seconds at a distance of 7.5 in. from the light source.

TABLE II. EFFECT OF ULTRAVIOLET LIGHT ON SIZING EFFECTS OF INDUSTRIAL 4022 CONDENSATE Handsheets exposed to Handsheets kept in the dark ultraviolet light 2 Normal procedure 9 Cobb size, g./ Cobb size, g./ Cobb size, g./ m. /3 minutes m. /3 minutes mJ/S minutes 10% Ink 10% Ink 10% Ink Conditioning lactic flotation, lactic flotation lactic flotation Condensate time 4 ater acid seconds Water acid seconds Water acid seconds Alkali-treated 24 hours 46 5.1.. S-I 34 28 900 33 64 250 t0 900 l Handsheets were prepared from 85-brightness kraft pulp, sized with 0.5% of the condensate.

2 After drying the handsheets (screen side only) were exposedfor 3 minutes at a distance of 7.5 inches.

3 No attention was given to exposure to light during preparation or conditioning.

4 The handsheets were dried minutes at 135 0., then conditioned at 23 C. and RH for the times indicated before sizing measurements were made.

l The fatty acids were heated under reduced pressure in the presence of boron trifluoride etherate catalyst. The condensate was not alkali-treated.

2 Saturated immediately.

TABLE IV.IRRADIANCE, TOTAL ENERGYHAND SIZING RESULTS FOR DIFFERENT KINDS OF L1G T EXPOSURE l Penetration times, seconds, Total after the indienergy, cated light wattexposure Irradiance, Exposure seconds/ w ts e, cm. 10% lactic Light source Filter cm. (10' seconds X10- acid Ink Hanovia ultraviolet lamp, 325 watt ..{%f; g &' 62 28 :3 3? 288 None 10 30 300 600 900 Yellow 8. 2 30 246 2 83 General Electric R. S. Reflector Sunlamp, 275 watt Blue 5 1. 9 46 87 442 900 Ultraviolet. 0. 11 46 5. 1 206 720 None 6 41 30 1, 230 337 900 General Electric BFA Photofiood lamp, 375 watt Yellow. 6 32 30 960 130 762 Blue 3. 9 46 180 151 762 Handsheets sized with 0.5% or industrene 4022 Condensate exposed to the indicated light source.

2 The handsheets were exposed to the Hanovia lam at a distance of 7.5 in. from the filter holder. The handsheets were expgsed to the Sunlamp and the Photoflood lamp at a istance of 7.5 in. from the envelope.

anovia 360 mn filter. (Transmits primarily 350-375 mp. radiation.)

4 A Corning 3387 yellow filter, 440 mu sharp cut-off, 90% transmittance from 560 to 760 mp. A Coming 5547 blue filter, 350 m to 560 mp transmittance, maximum at 420 my.

9 Subject to error because of the extremely high values.

TABLE V.THE IRRADIANCE AT VARIOUS DISTANCES FROM THE HANOVIA LAMP, AND THE SIZING OBTAINED WITH INDUSTRENE 4022 CONDENSATE 1 1 Handsheets, sized with 0. 5% of Industrene Condensate were exposed to the Hanovia ultraviolet lam at the distances indicated. The sizing results are repeated from Table Report 55.

I The distances were measured from the center of the Hanovia mercury tube to the surface of the paper.

While the invention has been described with particular reference to specific embodiments it is to be understood that it is not to be limited thereto but rather is to be restricted solely by the scope of the appended claims.

We claim:

1. In a process for the internal sizing of paper which comprises forming an aqueous slurry of paper pulp, treating the slurry by admixing therewith the condensation product obtained by heating (a) in the presence of a catalyst selected from the group consisting of boron trifiuoride, boric acid, boric oxide, ammonium pentaborate, trimethyl borate, triethyl borate, mannitol boratc, and the mixed anhydrides of boric acid and fatty acid at least one fatty acid of the formula RCOOH (b) wherein R is an unsubstituted long chain hydrocarbon radical containing f'rom 9 to 25 carbon atoms said condensation product being further characterized by at least 32% by weight of unsaponifiable matter and by having a mean molecular weight of at least 3 times that of said acid, and then forming the treated paper pulp into sheets, the improvement comprising exposing the sheets to actinic light sufiicient to supply at least enough radiant energy thereto to achieve a sized paper having an ink flotation time in excess of 900 seconds and a lactic acid penetration time in excess of 600 seconds.

2. The process of claim 1 wherein the radiant energy is sufiicient to supply at least about 6X10 watt-sec./ cm. to the sheets.

3. The process of claim 2 wherein said actinic light is ultraviolet light.

4. The process of claim 1 wherein said actinic light is References Cited UNITED STATES PATENTS 1,542,539 6/1925 Wright 162192 X 3,306,812 2/1967 Sinclair et a1 l62-179 X 3,404,064 10/1968 Feazel 162179 S. LEON BASHORE, Primary Examiner F. FREI, Assistant Examiner US. Cl. X.R. 

